Lighting applications based on occupancy and/or motion sensing are known, in which one or more lighting fixtures provide illumination in a space/area based on detection of object movement and/or presence of a person in the space/area. Various sensitivities may be provided for a range (e.g., distance/area) around the lighting fixture(s) in which detection of motion and/or a presence of a person triggers the lighting fixture(s) to turn on so as to illuminate the space/area. In any event, in terms of providing illumination based on occupancy/motion sensing, control of the lighting fixture(s) is limited to switching the lighting fixture(s) between full-on and full-off lighting states.
In connection with occupancy sensing, occupancy sensors use different technologies to detect the presence or absence of people in a space, including passive infrared (PIR), ultrasonic, and dual-technology. In many situations, it is desirable (but not necessary) for lighting to be activated as soon as a person/object of interest enters a particular area of interest. PIR sensors sense the difference in heat emitted by humans in motion from that of the background space. These sensors detect motion within a field of view that generally requires a line of sight; they cannot “see” through obstacles and have limited sensitivity to minor (hand) movement at distances typically greater than 15 feet. The sensor is most sensitive to movement laterally across the sensor's field of view, which can be adjusted.
PIR sensors generally are most suitable for smaller, enclosed spaces (wall switch sensors), spaces where the sensor has a view of the activity (ceiling- and wall-mounted sensors), and outdoor areas and warehouse aisles. Potentially incompatible application characteristics include low motion levels by occupants, obstacles blocking the sensor's view, mounting on sources of vibration, or mounting within 6 feet to 8 feet of HVAC air diffusers.
Ultrasonic sensors use the Doppler principle to detect occupancy through emitting an ultrasonic high-frequency signal throughout a space, sense the frequency of the reflected signal, and interpret change in frequency as motion in the space. These sensors do not require a direct line of sight and instead can “see” around corners and objects, although they may need a direct line of sight if fabric partition walls are prevalent. In addition, ceiling-mounted sensor effective range declines proportionally to partition height. Ultrasonic sensors are more effective for low motion activity, with high sensitivity to minor (hand) movement, typically up to 25 feet. The sensor is most sensitive to movement to and from the sensor. Ultrasonic sensors typically have a larger coverage area than PIR sensors. The sensor's view cannot be adjusted.
Ultrasonic sensors are most suitable for open spaces, spaces with obstacles, restrooms, and spaces with hard surfaces. Potentially incompatible application characteristics include high ceilings (greater than 14 feet), high levels of vibration or air flow (which can cause nuisance switching), and open spaces that require selective coverage (such as control of individual warehouse aisles).
Dual-technology sensors employ both PIR and ultrasonic technologies, activating the lights only when both technologies detect the presence of people, which virtually eliminates the possibility of false-on, and requiring either one of the two technologies to hold the lights on, significantly reducing the possibility of false-off. Appropriate applications include classrooms, conference rooms, and other spaces where a higher degree of detection may be desirable.
For effective occupancy sensing, generally required coverage area and required sensitivity are coordinated by a lighting designer/engineer. Generally the designer must determine range and coverage area for the sensor, based on the desired level of sensitivity. Manufacturers of sensors publish range and coverage area for sensors in their product literature, which may be different for minor (hand) motion and major (full-body) motion. Various coverage sizes and shapes are available for each technology. In a small space, one sensor may easily provide sufficient coverage. In a large space, it may be desirable to partition the lighting load into zones, with each zone controlled by one sensor.
In some instances, after presence or motion is no longer detected, the lighting fixture(s) may transition from a full-on to a full-off state (so as to no longer provide illumination) according to one or more predetermined or fixed options for a transition delay between the on and off states. Such a delay often is manually set via a switch, dial, or other user interface on a lighting fixture itself. In many conventional lighting applications involving fluorescent or HID lighting fixtures, for example, minimum times for such transition delays are determined in significant part by operating characteristics and requirements for the fixtures. For example, according to exemplary warranty requirements associated with fluorescent and HID fixtures, these fixtures are recommended to remain in an on-state for a minimum amount of time (e.g., on the order of 10 to 15 minutes) so as to mitigate functional wear and tear on the electrical and lighting components and reduced fixture life.